(1) Technical Field
The present invention relates to image forming devices, and in particular, to a technology for providing an image forming device that achieves a duplex printing function, a small size, and high productivity all at the same time.
(2) Related Art
Typically, an image forming device such as a copy machine has a scanner unit and a printer unit that forms images on recording sheets. Further, in a specific type of image forming devices, the printer unit is located below the scanner unit with a space (referred to in the following as an in-body space) between the scanner unit and the printer unit, and recording sheets output from the printer unit are ejected within the in-body space before further processing. Such an image forming device is commonly referred to as an in-body paper-ejection type image forming device.
An in-body paper-ejection type image forming device may include a post-processing device that performs post-processing (e.g., stapling) with respect to stacks of recording sheets. Further, the post-processing device may be located within the in-body space. In such an image forming device, a recording sheet stack having undergone post-processing by the post-processing device may, for example, be eventually pushed out towards a tray (referred to in the following as a front tray) provided at the front side of the image forming device.
However, in such an image forming device, when a first recording sheet stack and a subsequent second recording sheet stack are to be continuously post-processed, the second sheet stack cannot be ejected to the in-body space while the first recording sheet stack is being post-processed and resides within the in-body space. Thus, image forming with respect to the second recording sheet is suspended until post-processing of the first recording sheet stack is completed and the first recording sheet stack no longer resides within the in-body space. This results in the image forming device having low productivity.
In view of this problem, conventional technology (for example, Japanese Patent Application Publication No. 2006-096546) proposes an image forming device that includes, along a path extending from a fixing unit to a post-processing tray, a buffer means for temporarily holding recording sheets. FIG. 13 exemplifies such an image forming device. Providing such a buffer means enables performing image forming with respect to recording sheets belonging to a recording sheet stack (i.e., prevents the suspension of image forming as described above), even when a previous recording sheet stack still resides on the post-processing tray. Thus, an in-body paper-ejection type image forming device with such a buffer means has higher productivity than a similar image forming device without such a buffer means.
However, in the image forming device pertaining to the conventional technology described above, the buffer means, the post-processing tray, and a first paper eject tray are disposed in the stated order along a transport path of recording sheets. Due to this, a recording sheet bearing an image travels a relatively long distance to reach the first paper eject tray. Thus, the image forming device has a large size.
In addition, the image forming device pertaining to the conventional technology described above includes a second paper eject tray that is separate from the first paper eject tray. The second paper eject tray is used in duplex printing and changes the transport direction of a recording sheet from a first transport direction to a second transport direction, in order to change the image-forming target side of the recording sheet. The image forming device, due to having two paper eject trays as described above, inevitably has a large size.